This new version brings enhancements and simplification to the previous v. 2.
To start supporting v. 3. on my own projects as soon as possible I started the following initiatives:

Build a OpenAPI library for TypeScript to help building API contracts for v.3. https://github.com/metadevpro/openapi3-ts it includes a small fluent DSL to build your contract and explore v. 3 building blocks.

Build a plugin for one of my favourite libs: baucisJS The library is called baucis-openapi3 and as you will probably guess, yes it adds OpenAPI contracts to your API built with baucis.